Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1053 AM EST Sat Dec 22 2018 Valid 12Z Tue Dec 25 2018 - 12Z Sat Dec 29 2018 ...Significant central U.S. storm after Christmas... ...Overview... A storm system moving through the Southwest states next Tuesday (Christmas Day) will lift through the central Plains Wed-Thu and intensify, setting the stage for a major rain and snowstorm for much of the center of the country. The system will move into the Great Lakes on Friday and then off the Northeast/Mid-Atlantic coast next Saturday as another storm moves through the West/Southwest and Texas. The large scale remains quite predictable but the important details will be refined over the next several days. ...Guidance Evaluation/Preferences... A majority deterministic model blend (including the 00Z ECMWF/GFS/FV3) served as a good starting point during days 3-5 (Tue-Thu) given the good ensemble agreement through the end of the forecast period, with increased weight placed toward the 00Z ECENS/NAEFS means by days 6-7 (Fri-Sat). The 06Z GFS eventually became faster than the guidance consensus with the progression of the low pressure system through across the Great Lakes Fri-Sat, so the 00Z GFS (which was right in line with the consensus) was used instead. Overall, only minor changes to continuity were made as the overall consensus blend has been fairly steady. ...Weather Highlights/Hazards... Early in the week the precipitation focus will be on the Southwest as the Pacific system pushes through northern Arizona. As the system starts to lift northeastward through Kansas, precipitation will expand around and ahead of the deepening low with the flow out of the Gulf. To the northwest of the surface low, snow will come down heavy at times with increasing wind and possible blizzard conditions over parts of Kansas and Nebraska Thursday. Several inches of snow are likely over a large area with over a foot quite possible for some areas. Please consult the latest winter weather probabilities for a daily graphical depiction. In the warm sector, rainfall could become locally heavy near the Gulf Coast as the system infuses Gulf moisture northward up and over the warm front. Temperatures will trend cooler than average in the West behind the front Tuesday but will be above average over the Plains and much of the East as high pressure moves off the Mid-Atlantic coast. As the surface low deepens over Kansas, milder air will be drawn northward from the Mississippi Valley eastward as the synoptic warm front and leading warm front surge northward. This will yield temperatures 10-20 deg F above average, especially overnight, progressing eastward ahead of the cold front. Ryan/Fracasso WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml